Because I had no idea what it was:

    Gallium3D is a software library for 3D graphics device drivers being
    developed by VMware, after they acquired Tungsten Graphics[1]—the original
    authors.
    
    The Gallium3D library operates as a layer between the graphics API and the
    operating system with the primary goal of making driver development easier,
    bundling otherwise duplicated code of several different drivers at a single
    point (this is done by providing a better division of labor, for example,
    leaving memory management to the kernel DRI driver) and to support modern
    hardware architectures.
    
    Gallium3D is currently used by the free and open source nouveau graphics
    driver.

http://en.wikipedia.org/wiki/Gallium3D